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Time filter

Source Type


Sun H.,Xian University of Arts and Science | Li Y.,Xian University of Arts and Science | Yuan H.,National Time Service Center
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2010

At 2002, Japan decided to establish the quasi-zenith satellite system (QZSS). The system will supply advanced methods for the positioning and navigation and for the next-generation mobile communication. The construction of the system will be accomplished at 2011. The establishment background and the functions of the system, the roles of the system in GPS augmentation, and the time tasks in the system are analyzed. Source


Xu B.,Nanjing University | Wang Y.,Aerospace System Engineering Shanghai | Yang X.,National Time Service Center
Studies in Computational Intelligence | Year: 2013

In order to improve navigation satellite clock error prediction accuracy, a hybrid model is proposed in this paper. According to the physics property of atomic clock, the model firstly fits the clock error series by polynomial model. Then it models for polynomial fitting residuals, using functional network. The functional network structure is defined by wavelet de-noising and phase space reconstruction. Finally the GPS satellites are taken for example and four separate predict tests are done, the simulation results show that the proposed method can fit and predict the clock error series effectively, whose predict accuracy is better than those of IGU-P and conventional methods. © Springer-Verlag Berlin Heidelberg 2013. Source


Xu B.,Nanjing University | Wang Y.,Shanghai Aerospace System Engineering | Yang X.,National Time Service Center
Neural Processing Letters | Year: 2013

The high precision prediction of atomic clocks on board is a key technology for the long-term autonomous operation of a navigation satellite system. Some researches show that the performance of traditional prediction models of atomic clocks can not meet the requirements of practical applications. In order to improve the atomic clock error prediction accuracy, we propose a model based on functional network in this paper. According to the data characteristics of atomic clocks, the clock error series is firstly fit by polynomial and then the residuals is modeled by functional network. Finally, by using the data of GPS satellites, five independent prediction tests have been done to verify the model. The simulation results show that, compared with the traditional models, the proposed model can fit and predict clock error more effectively. © 2012 Springer Science+Business Media New York. Source


Yao Y.,Xian University of Posts and Telecommunications | Yao Y.,University of Chinese Academy of Sciences | Zhang S.G.,National Time Service Center
Applied Mechanics and Materials | Year: 2014

This paper proposed two kinds of precepts on time comparison for SDH network in practice. The precepts are the method of double-end bi-directional and the method of single-ended one-way. The computational model and network configuration of those precepts are given in this paper. Through the first precept, the time delay of fiber transferring can be got also, so the method can be used to time deliver too. © (2014) Trans Tech Publications, Switzerland. Source


Wang Y.,Nanjing University of Aeronautics and Astronautics | Xu B.,Nanjing University of Aeronautics and Astronautics | Xu B.,Nanjing University | Yang X.-H.,National Time Service Center
Yuhang Xuebao/Journal of Astronautics | Year: 2012

In order to improve the prediction accuracy and real-time performance of the navigation satellite clock error, a satellite clock error prediction method based on the combination of polynomial model and functional network is proposed in this paper. Firstly a polynomial model is used to fit the clock error series according to its physical property, and then the polynomial fitting residual is modeled based on the functional network, while the functional network structure is defined by using wavelet denoising and phase space reconstruction. Finally the GPS satellites are taken for example and four short-term prediction tests are done, and the simulation results show that the proposed method can be used to fit and predict the clock error series effectively, whose prediction accuracy is better than that of IGU-P ephemeris. Source

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